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7h
revised Union of subgroups is a subgroup if and only if one subgroup is a subset of the other
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7h
revised bounded operator $T$ is not compact then there exists an orthonormal sequence $e_n$ and $d>0$ such that $\|T(e_n)\|>d$ for all $n\in\Bbb{N}$?
appended answer 981594 as supplemental
14h
revised Finding number of homomorphisms from $\Bbb{Z}_m$ to $\Bbb{Z}_n$
rolled back to a previous revision
23h
revised Why is there apparently a consensus on the P = NP question?
improved formatting (perhaps)
1d
revised Find absolute maximum and minimum with domain
edited tags
2d
comment How do we know ternary expansions with only $0$'s and $2$'s are unique?
@rehband: First note that the series both converge. Since $c_n\leq 2$, then clearly $\sum_{n=N+1}^\infty c_n3^{-n}\leq\sum_{n=N+1}2\cdot 2^{-n}$. The equality just comes from the formula for the sum of a geometric series $\sum_{n=0}^\infty a\cdot r^n=a\cdot\frac 1{1-r}$. In this case, $\sum_{n=N+1}^\infty 2 \cdot 3^{-n} = \sum_{n=0}^\infty \frac{2}{3^{N+1}} ( \frac{1}{3} )^n$, so $a = \frac{2}{3^{N+1}}$ and $r = \frac{1}{3}$, giving the sum $a \cdot \frac{1}{1-r} = \frac{2}{3^{N+1}} \cdot \frac{1}{1-\frac{1}{3}} = \frac 1{3^N}=3^{-N}$.
2d
revised Countability for Subset of Irrational Number
edited tags
2d
revised Permutaion and Combination Problems
rolled back to a previous revision
2d
revised Permutations and Combinations? 3 digit number…
rolled back to a previous revision
2d
revised Permutations and Combinations. Arranging things to be adjacent etc…
rolled back to a previous revision
Oct
20
revised How to fix the order of AxesLabel in Mathematica 7.0 plot
pre-migration clean up (kinda)
Oct
20
comment Surjective homomorphism of rings. Every ideal of B is an extended ideal of an ideal of A.
You appear to have created numerous accounts on math.SE, each of which is unregistered. Consider registering an account so that you keep control of your content and account when you visit the site from different computers/devices. (If you still have access to this account, you can register it by adding an OpenId provider to the "my logins" section of your user profile.)
Oct
20
revised What to do with a random variable when we know its mean and variance but does not know which distribution it is?
rolled back to a previous revision
Oct
20
revised Regular Octagon Area
rolled back to a previous revision
Oct
19
revised Is every linear ordered set normal in its order topology?
formatting changes (mostly fixed-up a scrambled-up bit)
Oct
17
comment Minimum number of attempts to guess a PIN code, given constraints
@alexqwx: Even if you think he started it, this doesn't permit you to respond in kind. If someone is being abusive FLAG. This site is pretty much impossible to moderate without users FLAGGING bad behaviour. (Also, if you don't want to be suspended don't act in ways that are likely to get you suspended. It's really simple.)
Oct
17
comment Minimum number of attempts to guess a PIN code, given constraints
@alexqwx and Asaf: Quit it! Both of you!
Oct
17
comment Is $\omega_1$ metrizable?
Just a couple of comments. (1) An alternative way of showing that $\omega_1$ is not second-countable is to note that $\{ \alpha+1 \}$ is open in $\omega_1$ for all $\alpha < \omega_1$, and so any base for $\omega_1$ must contain all of these uncountably many singletons. (2) In metrizable spaces the notions of compactness, countable compactness, and sequential compactness are equivalent. (So $\omega_1$ is not metrizable since it is sequentially, and countably, compact, but not compact, or even Lindelöf.)
Oct
17
revised Trig height problem using elevation and shadow length?
MathJaxified
Oct
16
awarded  logic